1. Field of the Invention
The present invention relates to an optical pickup for reading recorded information from an optical information storage medium such as a compact disc, a laser video disc, or the like, and a tilt control device for use with such an optical pickup.
2. Description of the Prior Art
Some optical pickups for reading recorded information from an optical information storage medium such as a compact disc, a laser video disc, or the like have a tilt detecting device for detecting whether a light beam emitted from a light source is applied perpendicularly to the recording surface of the optical information storage medium.
One tilt detecting device for use with an optical pickup is shown in FIGS. 1(A) and 1(B) of the accompanying drawings. As shown in FIGS. 1(A) and 1(B), the tilt detecting device, generally designated by the reference numeral 200, has a semiconductor laser 31 for emitting a laser beam toward an optical disc DK, two photodetectors 32, 33 for detecting and photoelectrically converting a light beam reflected from a recording surface S.sub.2 of the optical disc DK into detected electric signals, and a differential amplifier 34 for calculating the difference between the detected signals from the photodetectors 32, 33 to produce a tilt error signal TE indicative of whether the laser beam is applied perpendicularly to the recording surface S.sub.2 of the optical disc DK.
If the semiconductor laser 31 and the photodetectors 32, 33 face properly to the optical disc DK, as shown in FIG. 1(A), then the two photodetectors 32, 33 detect equal intensities of the reflected light beam, and hence the differential amplifier 34 produces output signal of zero. If the optical disc DK is tilted with respect to the semiconductor laser 31 and the photodetectors 32, 33 as shown in FIG. l(B), the photodetector 32 detects a higher intensity of the reflected light beam than the photodetector 33, so that the differential amplifier 34 produces a positive output signal, thus detecting the tilt of the optical disc DK. A suitable control unit including an actuator may be connected to the tilt detecting device 100, thus making up a tilt control device for correcting the position of the optical pickup so that the laser beam will be applied perpendicularly to the recording surface S.sub.2 of the optical disc DK.
The tilt control device is disadvantageous in that its semiconductor laser 31 and the photodetectors 32, 33 are required in addition to the optical pickup which is used to reproduce an information signal recorded on the optical disc DK. Therefore, the entire assembly of the optical pickup and the tilt control device has a complex structure and a large size.